PORTLAND – The state’s first smallpox vaccinations for hospital workers, which had been scheduled for Monday, were canceled because of concerns about possible fatal side effects of the immunization.

Dr. Dora Anne Mills, director of the state Bureau of Health, said she suspended the vaccination program until authorities learn more about three deaths in other states, which appear to be heart attacks and may be related to the vaccine.

About a dozen vaccinated people have also developed inflammation in their hearts or heart lining, a relatively mild condition which experts believe is related to the vaccine.

“One naturally wonders whether the three people who died might have had inflammation of the coronary arteries and hence a heart attack, a fatal heart attack. We don’t know, … but we’ll have more information soon, based on autopsy results,” Mills said.

Depending on what the autopsies determine and on how many people get the heart inflammation, more people could be excluded from receiving the vaccine or the entire program could be postponed, Mills said.

The Bush administration’s smallpox vaccination program called for public health workers to be vaccinated first. Thirty-nine people in Maine, mostly Bureau of Health employees, have gotten the shots, Mills said. None developed any serious side effects.

But a much larger group of first responders is scheduled to get the vaccinations next.

“There are a lot of men in their 50s among the first responders,” Mills said. “And men in their 50s have risk for heart disease.”

All three people who died from heart attacks had risk factors for heart disease.

Initially, public health authorities expected that 10 to 15 people out of every million who got immunized would develop serious complications and that two out of every million would die.

Since about 375,000 Americans have been vaccinated since February, and heart disease is the leading cause of death in the United States, the three deaths might have been unrelated to the vaccine.

Mills noted that the last full risk studies of the vaccine were performed in 1968. “The tests for diagnosing heart inflammation are much more sophisticated now,” she said.

More than 30 hospital workers had been scheduled to receive the vaccine Monday at Maine Medical Center.

California, Illinois, New York and Vermont have also temporarily suspended their vaccination programs.